Method of removing foreign coatings from tinplate and the like



Sept. 30, 1958 w. s. FULKERSON- 2,854,361

' METHOD OF REMOVING FOREIGN COATINGS FROM TINPLATE AND THE LIKE Filed Sept. 9, 1955 INVENTOR Mum/v5 HAM-A 50 T ORNEYS METHOD OF' REMOVING' FOREIGN COATINGS FROM TINPLATE AND THE LIKE William S. Fulkerson, Hayward, Calif., assiguor of onehalf to Morris Horwitz, Oakland, Calif.

Application September 9, 1955, Serial N.'533,276

lz Claims. (Cl.-13430) This invention relates to the treatmentfiof tinplate, and

ismore particularly directed to apro'cess' for removing coatings of enamel, lacquer, lithographioi'nk and other "materials which might be placed'on'the'tinplate'sheets "during can manufacturing'or other operations.

As is well known in the art, tinplate consists of sheet Isteel provided with a thin coating of tin, the latter serving to protect the steel from" corrosion. Probably the widest use'of tinplate is for the'manufacture of cans, often referred to as tin cans. In the manufacture of 'such cans, large sheets of tinplate are used, anenamel,

varnish or lacquer coating maybe placed on the"surface which will form the inside'of he subsequently formed can body, and the other surface may be likewise coated and/or imprinted with ink. The thus'coated sheets are then cut into blanks from which the can'bodies are formed.

Notwithstanding the use of good coating and printing equipment, as well" as careful quality control, in

many cases,f theorigin'al sheetsof tinplate, upon inspec- "tion, will be found tohave displacedorotherwisedefective coatings of'lacquerorthe like, or-the printed material will not he properly positioned on the sheets. Heretofore, whenthis has occurred, the'sh'eetsof tin- *plate have been discarded and sold for salvage. There is a"substantial" difference between the cost of'tinplate sheets and the salvage-price on spoiled-sheets, and it has been estimated that 'the losses resulting from thisdiffer- "ential in the can makingindu'stry alone 'run'intoniillions of dollars annually.

-It' is therefore an -object of thepresent invention to provide a method 'or: process for reclaiming the -spoiled tinplate sheets, wherein the inks, lacquers; varnishes "and the like which were applied-to the sheets, may be readily and economically removed therefrom.

plate reclaiming process as above described 'which will -p'e'rmit the use of heretofore spoiled tinpla'te shee'ts in the same manner and with the sameeffectiveness as new sheets.

The invention possesses other objects and features of Unit States of the 'coating from the sheet.

2,854,361 Patented Sept. 30, 1958 2 permitthe recoating of'suchsheets where the original coating was in any way defective. As above suggested, there are'many reasons why the surface coatings might 'be defective, for example, the coating covering all or a portion of the surface where the body seam is to be made, the'coating beingirregular or spotty, the lithographic printing being unclear or not properly positioned, etc. Usually, before such defects have been discovered, a large number of full-size sheets will already have been coated and/or printed, and therefore there is a great need for some means of reclaiming these relatively expensive sheets foractual use rather than disposing of them for salvage. It'will become clear that the process about to 'be described can be used where the base sheet is not'tinplate, but, for example,- a plain steel plate. However, in the case of steel plates, the initial cost more closely approximates the salvage value than where tinplate is involved.

With reference to the diagram of the figure, a tinplate sheet'6 is illustrated in step A, with a defective coating 7 of varnish, lacquer, enamel, or other conventionally with-the present-invention may be reclaimed and reused.

The first step in my. process is to take the: coated sheet andimmerse 'the same in .acbath 8 of isopropyl-monoethanolamine which may be contained inla tank 9, as

shown in stepB. This bath, when maintained atthe proper temperature, serves to loosen the coating 7 from the sheet' 6,-and mayractually'etr'ect .a'complete peeling It is'extrernely important to control notonly the temperature of the bath, butthe time:of=sheet immersion as well. A short immersion period .and/or'ztoo vlow a-bath temperature will be inef- "fective in looseningorpeeling'the coating from the sheet. Conversely,1.'toolong-an immersion period and/or too high a bath'temperature will readily remove the coating,

but will result .inzstains or otherdisturbances' of the tin :il'ayeron itsrbasezmaterial, and render the tinplate sheet unusable :for can manufacture.

' .The minimum efiective temperature for the isopropyl- -monoethanolamine bath is 140 F.for removal of cer- .tain coatings without injury to the tinplate.

By way of 5example,xconventionally usedvarnish coatings and lithoadvantage, someofwhich,with the foregoing will be set -.forth.-in the following description of. preferredforms. of the invention. "It "is""to"be" understood, however, that Igraphiciinkswillcbe readily loosened or removed by contact withrtherbath for approximately 4 minutes, with the-bathatemperaturev maintained atl40 F. Lacquer coating-"removal requires an immersion period of approximately 8i'minutes'with a bath temperature of about 170 .F. Also, where the tinplate. sheet was manufacturedibythe hot. dip'method Ihave found that immerysion1in a- F.bath for approximately 12 minutes is effective in eliminatingthe stains otherwise found on such sheets. The foregoing temperatures and time periods are naturally dependent to some extent on the thickness of the coatings, but represent actual test figures for conventional can coatingthicknesses and materials. If the sheet 6 was plain steel ratherlthan tinplate, the bath temperature could be materially increased, thereby requiring a shorter immersion period, without causing any damage to the sheet.

Thus, in step B, the coated sheet is immersed in a bath of isopropyl-monoethanolamine, maintained at a temperature of l40-170 F. for a period of from 4 to 12 minutes to effect loosening or peeling of the coating 7 from the sheet.

While the above bath is effective in performing its requisite functions, it is also toxic and must be thoroughly and promptly removed from the tinplate before the latter may be reprocessed. Therefore, in steps: C and D,

the sheet is washed with water, which may be sprayed on the sheet, or as indicated in the drawlng, the sheet is placed in a tank 12; containing water 13. The-water is maintained at a temperature. of approximately. 140? F. during the washing operation for optimum results. Also, during the washing operation, the sheet isbrnshedwash tank 14 may be utilized to insure thorough cleansing of the sheet. Obviously, any suitable strainer or filter systemcould be incorporated in tanks 9, 12 and 14 so so as to completely remove any traces of the coating ,from the sheet. .If desired, and as shown, a second that the removed coatingmay be continuously or pei riodically removed from the solutionS or water 13. As

i such systems are conventional in the-art, and constitute no independent part of my invention, no detailed ex:

planation is deemed necessary, and for the same reason, the thermostaticcontrols for the solution temperatures have not been illustrated.

Following the water bath, the sheet 6 will be completelyfree. of .any portions of the coating 7, but will naturally be wet. The wet sheets must bedried so :as to remove all traces of water which will stain tinplate.

' .Therefore,.instead of attempting to dry the sheets in more conventional manners,-I place the same-in a solul. A method ofremoving coatings of the character hat is claimed is:

described from metal sheets which comprises applying to saidcoatings a bath of isopropyl-monocthanolamine maintainedat a temperature of from 140 F. to 185 F. for from 3 to 12 minutes, washing said sheets with water to remove said bath, and then drying the sheets.

2. A method of reclaiming tinplate .by removing lacquer, varnish, inks and like coatings therefrom comprising: immersing said tinplate in a bath of isopropylmonoethanolamine to effect a loosening of said coating, washing bath liquid from the tinplate, and then drying the tinplate.

- 3. Themethod of removing lacquer, varnish, ink and the like coatings from tinplate which comprises the plac-- ingot said tinplate in a bath of isopropyl-monoethanolamine, maintaining the temperature of said bath at from 140 F. to 185 F., removing the tinplate from said bath, and then washing any traces of said bath and-said coating from the tinplate.

4. A method as set forth in claim 3 in whichsaid tinplate is kept in said bath fora period of from. 3 to 12 tion 16 of pure alcohol contained in a tank '17 to remove the water. The alcohol may be reused by using copper sulfate crystals to remove the water. from: the

alcohol.

After dipping the sheet in the alcohol bath, step E,

the sheet may be dried by a blast: of warm. air or the alcohol merely permitted to evaporate, in any event leaving a. dry sheet of tinplate in excellent condition forreceiving a new coating of varnish, lacquer or the like. The foregoing description sets forth the preferred method of. reclaiming tinplate, but it is appreciated that minutes. i

5. A method of removing oleo and phenoliclacquer:

coatings from tinplate which comprises heating a bath of isopropylmonoethanolamine to a temperature of approximately 160 F., immersing said coated tinplate in said .bath for approximately 10 minutes, removing said tinplate from said bath, applying a water bath at a temperature of about 140 F..to said tinplate, and then drying'the tinplate.

changes might be madewhichwould possibly be .efiective. coated sheet in bath 8 could be materially reduced by raising the temperature to say 185 F. This would result in staining the tinplate, but for many manufactur- By way of example, the time of immersion of the 6. The: method set forthin claim 5 further characterized by said drying includingthe immersion of the tinplate in an alcohol solution to remove the water. therefrom. t

7. The method of removing varnishcoatingsandilithm graphic inks from tinplate comprising heating a.bath.of

- isopropylmonoethanolamine to a temperature of approxiing operations, such staining would not render the tinplate unusable.

Also, for reasons of illustration, 8 into which the defective sheets are placed, has been identified only as isopropyl-monoethanolamine, suchmaterial having been thoroughly tested for the purposes set forth. However, while no extensive tests have been conducted, preliminary considerations have indicated that the bath, at the temperatures suggested, could'be selected from other ones of the disubstituted amines where one substituent is ethanol and the other is an alkyl radical. Preferably, the alkyl radical contains from three to five carbon atoms, such as found in propyl, butyl and amyl respectively, and even more specifically, the branch chain radicals, such as isopropyl, isobutyl and isoamyl are pre the chemical hath ferred. Thus, in place of the isopropyl-monoethanol- H amine, the following liquids appearpractical for use, although with possibly diminishing effectiveness:

Isobutyl-monoethanolamine Isoamyl-monoethanolamine Monoalkylethanolamine Propyl-monoethanolamine Butyl-monoethanolamine Amyl-monoethanolamine said bath, and then drying the tinplate.

mately F., immersing said tinplate in said bath for approximately 4 minutes, washing said tinplate to remove coatings a liquid of a disubstituted amine where one substituent is ethanol and the other is an alkyl radical, heating said liquid to a temperature of from about 130 F. to F., and then washing the liquid from the tinplate.

10. A method as set forth in claim 9 in which said alkyl radical is selected from the group consisting of propyl, butyl, amyl, isopropyl, isobutyl, and isoamyl.

11. A method as set forth in claim 9 in which said liquid is a monoalkylethanolamine.

12. A method as set forth in claim 9 in which said coated tinplate is immersed in-said heated liquid for a period of from 3 to 12 minutes.

References Cited in the file of this patent UNITED STATES PATENTS Heinecke Oct. 28, 1952 

1. A METHOD OF REMOVING COATINGS OF THE CHARACTER DESCRIBED FROM METAL SHEETS WHICH COMPRISES APPLYING TO SAID COATINGS A BATH OF ISOPROPYL-MONOETHANOLAMINE MAINTAINED AT A TEMPERATURE OF FROM 140*F. TO 185* 